The replacement of a natural lens with an artificial intraocular lens implant in the human eye has become a well known procedure to physicians specializing in ophthalmology. In such a procedure, a corneo-scleral incision is made in the eye through which the natural lens is removed and the artificial intraocular lens is inserted. The intraocular lens may be designed to be positioned within either the anterior or posterior chamber of the eye.
Intraocular lenses typically include a central lens section, referred to as the optic, for focusing light onto the retina. One or more supporting structures, called haptics, extend outwardly from the optic to align and stabilize the optic with respect to the pupil. Typically, the haptics comprise one or more filamentous or wire-like arms or loops which extend radially outwardly from the periphery of the optic. The haptics may be fixed in position within the eye by sutures or by engagement with predetermined eye tissues.
Installation of an intraocular lens should be permanent so that subsequent surgical adjustments are not required. Accordingly, the reliability of the haptic is of great importance. The materials of construction and the design parameters must be selected such that the haptic can endure significant stresses with minimum risk of breakage. Moreover, the haptic must be capable of functioning safely in the presence of small stress risers, such as notches or nicks, which may be inflicted during handling and manipulation.
Unfortunately, haptics often develop clusters of fractures, referred to as craze, when subjected to impact and bending forces during handling. If the individual craze fractures are large enough to extend across a significant portion of the shaft diameter, a broken haptic results.
For intraocular lens haptics, there is concern that inadvertent impacts and stresses encountered in service may result in the development of relatively large craze flaws which could eventually lead to failure. Even if breakage does not occur, the existence of sizeable craze fractures that may extend to the surface of the haptic would be of concern from a biocompatibility point of view.